DESCRIPTION (Verbatim from the applicant's abstract): The endoplasmic reticulum (ER) is the compartment where membrane and secretory proteins are modified, folded, and assembled. In this capacity, the ER contains biochemical machinery for protein folding as well as quality control systems that either retain incompletely folded proteins in the ER or concentrate completed proteins into transport vesicles for export to distal compartments. Dr. Kaiser's research group proposes a combination of biochemical and genetic experiments in the yeast S. cerevisiae to give fundamental insight into the mechanisms of folding and quality control in the ER. Previous work in Dr. Kaiser's laboratory has delineated the core pathway in the ER for protein disulfide bond formation in which the luminal protein Erol transfers a disulfide bond to protein disulfide isomerase (PDI) which in turn transfers its disulfide bond to a substrate protein. More recently, the lab has identified a pathway for oxidation that operates in parallel to Erol and is based on the protein Erv2. In this application, Dr. Kaiser proposes to determine how the disulfide bond formation pathways are integrated with the redox chemistry of the cell and to elucidate the mechanism of disulfide transfer from Ero 1 and Erv2 to PDI and its homologs. These studies will include structural analysis of Erol and Erv2 as well development of in vitro reconstruction of the pathway for disulfide bond formation. Additional studies are planned to find new genes involved in either concentration of proteins into transport vesicles or in the retention of incompletely folded proteins. A failure in proper protein folding in the ER is the root cause of a number of diseases; cystic fibrosis being the best-studied example of an ER storage and folding disorder. However, we do not yet understand the molecular mechanisms that underlie dysfunction of folding and quality control. In S. cerevisiae, it will be possible to apply the full power of a well-developed genetic organism to uncover the genes and proteins responsible for protein folding and quality control in the ER.